Ullerup's first role was that of Julia Brynn on the remake television series of Battlestar Galactica in 2006, which aired on the Sci Fi Channel.[2] She played Ashley Magnus in the first and second seasons of the television show Sanctuary until her character was written out. Her departure remained a topic of heated debate among fans, with many of them wanting her brought back in future episodes,[3] until the show was cancelled in 2012.

Ullerup speaks Danish and English. Her father held the title of Lord Chamberlain for the Danish Royal Family.[5] In 2008, she was found to have a benign but aggressive tumor wrapped around her spinal nerves. She underwent surgery to remove the tumor in 2009, at which time her coccyx and half of the sacrum of her pelvis was removed.[3] After about five months, she recovered enough to return to work.[6]